1. Field of the Invention
The present invention relates to a process for producing (meth)acrylic acid having crystallization operations.
2. Description of the Related Art
Conventionally, a process for producing purified (meth)acrylic acid from crude (meth)acrylic acid by purifying using a crystallization method has been known. In purifying the crude (meth)acrylic acid by crystallization, the crude (meth)acrylic acid is crystallized and the crystallized (meth)acrylic acid is melted, thereby obtaining the purified (meth)acrylic acid. On this occasion, it is preferred that a crystallization operation comprising a crystallizing step and a melting step is repeated multiple times for enhancing purity of the obtained purified (meth)acrylic acid.
(Meth)acrylic acid is known as a polymerizable substance, and there is a case that a polymerization inhibitor is added in the crystallization operation for preventing (meth)acrylic acid polymerization. For example, WO 2010/140530 (Patent Literature 1) discloses a process for producing purified (meth)acrylic acid comprising a melting step in which a (meth)acrylic acid crystal is melted by supplying a melt, to which a polymerization inhibitor has been added, to the (meth)acrylic acid crystal while circulating. In the process disclosed in the Patent Literature 1, the crystallization operation is repeated multiple times, and a polymerization inhibitor is added in the melting step of the last crystallization operation that is for obtaining the purified (meth)acrylic acid as a commercial product and a polymerization inhibitor is further added in the melting step of the preceding crystallization operation. Japanese Unexamined Laid-open Patent Application Publication No. 9-155101 (Patent Literature 2) also discloses a process for producing purified (meth)acrylic acid by repeating the crystallization operation multiple times. In the process disclosed in the Patent Literature 2, (meth)acrylic acid solution which has been prepared by adding a polymerization inhibitor to (meth)acrylic acid melt obtained by the k+1th crystallization operation is added in the melting step of the kth crystallization operation, and purified (meth)acrylic acid, to which a polymerization inhibitor has been added, is also added in the melting step of the last crystallization operation that is for obtaining the purified (meth)acrylic acid as a commercial product.